Now, a team led by Doctor Miguel Nicolelis, a professor of neurobiology, has taught rhesus monkeys to move both arms of an onscreen avatar just by thinking about it.

The team studied large-scale cortical readings from the monkeys to determine if they could provide sufficient signals to a brain-machine interface (BMI) for accurate bimanual movement -- and determined that the neuronal activity for bimanual movement is different from the activity for controlling only one arm at a time. It seems to be that large neuronal ensembles rather than single neurons are responsible for normal motor functions and that small neuronal samples of the cortex do not provide enough information for complex movements via BMI.

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"When we looked at the properties of individual neurons or of whole populations of cortical cells we noticed that simply summing up the neuronal activity correlated to movements of the right and left arms did not allow us to predict what the same individual neurons or neuronal populations would do when both arms were engaged together in a bimanual task," Nicolelis said. "This finding points to an emergent brain property, a non-linear summation, for when both hands are engaged at once."

The monkeys were then trained to control two arms in a virtual environment using a pair of joysticks, placing the virtual hands on a variety of objects. Then, the joysticks were taken away, and the monkeys were able to control both arms simultaneously with just their brain activity -- without moving their own arms at all.